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Hw I'm having pbms with

  1. Feb 21, 2006 #1
    http://img423.imageshack.us/img423/4778/hwhelp1bs.jpg [Broken]
    The first one on the left is a Multiple Choice question. Just the mention of variables shuts down my brain. I'm still researching for the equation for the pbm.

    The pbm in the right upper corner i think it's C and E. (by simply looking at it)

    The pbm on the bottom right corner i used -E times delta r... I got -17.59.

    Any help in the next 20-30 minutes will be much appreciated... as it'll double my hw score...
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Feb 21, 2006 #2
    Potential is a scalar quantity. The distance of the points in all the 3 cases from the charges is same (they lie on the perpendicular bisector). So the net potential will be zero along these points (all are equal = 0).

    For the right upper corner, consider the other point where the potential may be zero. There are three possibilites - right of +Q, between the charges and left of -2Q. One case is already given - right of +Q. Left of -2Q will be ruled out (Why?). So one case is left. Solve. (d/3)

    For 3rd one use E = - (V/d)
    or V = - E . d (E dot product d).
    where d is the radius vector pointing from B to A.
  4. Feb 21, 2006 #3
    For the second question answer is D+(2D/3) = 5D/3
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